Ultrasound waves have been widely used in medical applications. For example, ultrasound waves have been used for diagnostic and therapeutic purposes, as well as in many industrial applications. One diagnostic use of ultrasound waves includes using ultrasonic waves to detect underlying structures in an object or a human tissue. In this procedure, an ultrasonic transducer is placed in contact with the object or tissue and a coupling medium is used to help efficiently transmit the high frequency (1-10 MHz) ultrasonic waves that are directed into the tissue. Upon contact with various underlying structures, the waves are reflected back to a receiver adjacent the transducer. By comparison of the signals of the ultrasonic wave as sent with the reflected ultrasonic wave as received, an image of the underlying structure can be produced. This technique is particularly useful for identifying boundaries between components of tissue and can be used to detect irregular masses, tumors, and the like.
In addition to diagnostic uses, ultrasonic energy can be used for therapeutic purposes. Two therapeutic medical uses of ultrasound waves include aerosol mist production and contact physiotherapy. Aerosol mist production makes use of a nebulizer or inhaler to produce an aerosol mist for creating a humid environment and delivering drugs to the lungs. Ultrasonic nebulizers operate by the passage of ultrasound waves of sufficient intensity through a liquid, the waves being directed at an air-liquid interface of the liquid at a point underneath or within the liquid. Liquid particles are ejected from the surface of the liquid into the surrounding air following the disintegration of capillary waves produced by the ultrasound. This technique can produce a very fine dense fog or mist. Aerosol mists produced by ultrasound are preferred over aerosol mists produced by other methods because a smaller particle size of aerosol can be obtained with the ultrasonic waves. Although ultrasonic nebulizers represent an improvement over other nebulizer technologies, the use of ultrasound energy in this context has certain limitations. One of the major shortcomings of inhalers and nebulizers is that the aerosol mist produced cannot be directed to a target area without an air stream. However, the use of an air stream decreases the efficiency of ultrasound, thus limiting the utility and therapeutic applicability of ultrasound nebulizers.
Ultrasonic sprayers such as those sold by Sonic and Materials Inc., Misonix Inc., Sono-Tek Inc. (see, for example, U.S. Pat. Nos. 4,153,201, 4,655,393, and 5,516,043) operate by passing liquid through a central orifice of an ultrasound instrument-tip. Major disadvantages of these sprayers include non-uniform particle size, heating of liquid flow, and less efficiency of the ultrasound waves.
Contact physiotherapy applies ultrasonic waves directly to tissue in an attempt to produce a physical change in the tissue. In conventional ultrasound physiotherapy, an ultrasonic wave contacts the tissue via a coupling medium. Ultrasonic waves produced by the transducer travel through the coupling medium and into the tissue. The coupling medium is typically a bath of liquid, a jelly applied to the surface to be treated, or a water-filled balloon. Conventional techniques provide ultrasonic waves having an intensity of about 0.25 w/cm2 to about 3 w/cm2 at a frequency of about 0.8 to about 3 Megahertz. The treatment is applied to a skin surface for about 1 to about 30 minutes, for multiple times a week. The coupling medium can provide a cooling effect which dissipates some of the energy produced by the ultrasonic transducer.
More importantly, a coupling medium or direct contact between the tissue and ultrasonic transducer is desirable to transmit the ultrasonic waves from the transducer to the skin surface because ambient air is a relatively poor medium for the propagation of ultrasonic waves.
Several beneficial effects have been reported from contact ultrasound physiotherapy, such as, for example, the following: local improvement of the blood circulation, heating of the tissue, accelerated enzyme activity, muscle relaxation, pain reduction, and enhancement of natural healing processes. Despite these beneficial effects, current techniques of medical physiotherapy using ultrasonic waves are limited because the efficient transmission of the ultrasonic waves used in these technologies requires direct contact between the device and the tissue to be treated. This direct contact, even if via a coupling medium, may be undesirable for certain medical applications.
The requirement of direct contact, with or without a coupling medium, makes current contact physiotherapy methods and devices undesirable and suboptimal for many therapeutic uses. Although some tissue conditions may be physically accessible to contact ultrasound devices, the use of contact-mediated devices would be impractical and undesirable. For example, fresh or open wounds resulting from, for example, trauma, burns, and surgical interventions are not suitable for direct contact ultrasound treatment because of the structural nature of the open wound and the painful condition associated with those wounds. Moreover, conventional contact ultrasound may have a destructive effect on these types of open wounds due to the close proximity of an oscillating tip of an ultrasonic transducer relative to the already damaged tissue surface. Furthermore, open wounds are susceptible to infection and may already harbor significant bacterial and other microbial growth. Direct contact with the wound may increase the risk of contamination of the wound and/or the risk of contaminating the device or its operator.
Commonly-owned U.S. Pat. No. 6,569,099 discloses an ultrasonic device and method for wound treatment, the entire contents of which are incorporated herein by reference. This patent discloses, inter alia, a device that sprays liquid particles to a wound via an applicator. The liquid particles provide a medium for propagation of the ultrasonic waves. In contrast to prior art methods and devices for contact, ultrasonic physiotherapy, the applicators and devices disclosed in the present application, as well as the devices disclosed in U.S Pat. No. 6,569,099, provide non-contact methods for delivering ultrasonic energy via a liquid mist.
As can be appreciated, an improved applicator may be desired to produce a more reliable and consistent flow of liquid particles to a wound bed or site. The present invention provides an improved applicator that can be used in non-contact ultrasound therapy for the treatment of wounds.